The present invention relates generally to electro-optical inspection systems, and more particularly to an automated reticle inspection system and method for determining which defects in a reticle will print on the substrate and effect the performance of a completed semiconductor device.
Present reticle and photomask inspection systems currently identify defects on reticles and photomasks merely as defective pixels. No effort is made to determine printability and the ultimate impact of identified defects on a finalized semiconductor device. That approach has been satisfactory in the past given the trace widths and number of components to be implemented on a single substrate and in a single chip.
However new technology has continued to push the line and component density on a single semiconductor substrate, and in a single chip, to greater and greater levels with ever narrower line widths being required. That being true, and given the previous criteria as to what defects are a potential problem, smaller and smaller anomalies in reticles and photomasks are being considered a defect. Given the current technology, anomalies of well below one micron in size (down to 200 nanometers in some cases) are being considered defects. Therefore, inspection machines have been refined to detect these ever smaller anomalies on reticles and photomasks.
Currently, in the semiconductor industry, complex reticles and photomasks that can cost tens of thousands of dollars to produce are being scraped since it is believed that even the smallest defect in one reticle or photomask used in the production of a substrate may have a detrimental effect on the performance of the final semiconductor component.
What is needed is a method and system that not only identifies the ever smaller anomalies on a reticle or photomask as a defect; but which goes further and considers other characteristics, the location of the defect, and the line patterns on the reticle or photomask, to determine whether or not each individually identified defective pixel will print onto,the semiconductor substrate. If this is accomplished, many reticles and photomasks that are currently being scraped could instead be used with no detrimental effect on the operation of the final semiconductor component, thus reducing the cost of production of semiconductor devices. It is believed that the present invention provides that capacity.
The present invention includes a method and software program for determining printability of a defect on a reticle or photomask onto a substrate during processing. That is performed by creating a pixel grid image having a plurality of individual pixel images showing the defect. A gray scale value is assigned to each pixel image of the pixel grid image and a probable center pixel of the defect is selected. Then the polarity of the defect is determined, with a coarse center pixel of the defect optionally selected using the probable center defect and polarity of the defect. If a coarse center pixel is selected, then a fine center of the defect can optionally be selected from the coarse center pixel and polarity of the defect. From the center pixel the physical extent of the defect can be determined followed by the determination the transmissivity energy level of the physical extent of the defect. Optionally, the proximity of the defect to a pattern edge on the reticle or photomask can be determined using the physical extent and polarity of the defect. Then the printability of the defect can be determined from the transmissivity energy level of the defect and characteristics of the wafer fabrication process being used to produce the substrate from the reticle or photomask.